Developers, who had been limited to using software simulators of the watch, discovered new possibilities.

Ross Cohen, chief operating officer of BeenVerified.com, which makes a caller ID app for the watch, said he only realized on Friday that the watch goes on and off automatically as you raise or lower your wrist.

The simulator did not have a microphone, leaving some developers to guess how well it could hear. Having the watch on hand will speed development, said Danielle Keita-Taguchi, marketing analyst at Y Media Labs, which has designed apps for companies like American Express, EMC and eBay.

"A lot of Fortune 500 companies really want to leverage this new technology quickly," she said. "Health, transportation and social media will be the three main industries that will utilize the Apple Watch."

Ride-hailing service Uber had an app, as did sports network ESPN, microblogging platform Twitter, photo sharing service Instagram, tune-identifier Shazam and the Outlook email app from Microsoft Corp.

Notable absences included social network Facebook, message service Snapchat and any apps from Google Inc. So far developers see the watch's main benefits as saving time or the labor of frequently taking out a phone.